Population ecology and the conservation and management of Caiman yacare in the Pantanal, Brazil

Abstract

The Pantanal is one of the largest wetlands in the world (140,000 km2), with high conservation priority. It is located in the upper Paraguay river basin near the geographic centre of the South American continent. One of the features of the Pantanal is the abundance of Caiman yacare, distributed widely throughout the floodplain. Prior to 1967 there were no restrictions on the exploitation of wildlife in Brazil and the harvesting of caimans in the Pantanal was conducted at an industrial scale. In 1967, legislation passed by the Brazilian federal government prohibited the commercial harvest of caimans. Most of the people involved in the harvesting of caiman relied on that activity for their living, and the lack of alternative work and the high demand for skins in the international market led to the emergence of poaching and an illegal trade. Since 1990, management policy was redirected and, instead of adults, harvesting quotas of eggs from natural populations was allowed. The biological basis of such policy has not been evaluated and, currently, the use of caiman has been of little importance to promote socioeconomic development and habitat conservation in the Pantanal. The present study, which is part of a joint effort of Brazilian governmental and non-governmental institutions, further develops the biological knowledge required to improve the current management policy and aims to encourage wetland conservation and socioeconomic development through the sustainable use of caimans.In the introductory chapter, the basic ideas and concepts underlying the conservation and management of wildlife in both scientific and socioeconomic dimensions are summarized, and the scope and relevance of the project are identified.Chapter 2 describes the main features of the Pantanal wetland, the experimental site and the general methodologies used in the study. These are followed by a brief review of the taxonomic and current status of the caiman population in the Pantanal and, in a long story cut short, gives an account of the political qvoyageq to obtain ethical clearance for what was the first legal harvest of adult caimans in the Pantanal since 1967.Chapter 3 describes the feeding habits and how they change according to ontogeny and in response to seasonal changes in the environment. The ways in which feeding is related to body condition are investigated and easy-to-measure blood components are quantified and an index of parasitism is derived to determine whether they could be related to individual body condition.nThe caiman diet was dominated by insects, snails, crabs and fishes, whereas other prey, including cannibalism, had only minor importance. Most of the variation in feeding success, dietary composition and body condition could be explained by seasonal changes in water level and temperature. High water level and high temperature (Jan-Mar) were positively related to feedingnsuccess and most of the individuals preyed on vertebrates. When temperatures decreased and water level remains high (Apr- Jun), feeding success remained high but shift to invertebrates. The period of low temperature and low water level (Jul-Sep) was critical for body condition, given that feeding success was low during this period and the diet was composed mainly of invertebrates. When the temperatures increased and water level remained low (Oct-Dec), body condition might improve in response to the prevalence of vertebrates in the diet, but low feeding success counteracted this positive effect. The plasma components studied (protein, lipids, urea, phosphorus and calcium) and levels of parasitism did not show any simple relationship, nor was there any indication that they could be reliably used to predict individual body condition.Chapters 4 and 5 examine the interactions between reproduction, body condition and environmental variables. A detailed anatomical and morphological analysis of the gonads and accessory organs, complemented by studies on plasma steroid sex hormones, was undertaken. Also, the results of a 10 year study period on the nesting ecology and reproductive performance of the population are presented. The emphasis here is on temporal variation in the nesting season and habitat, nest production, female and clutch dimensions, nest losses and hatchling success and sex ratio. Such analysis provided the chance to examine the determinants of gonadal activity and some of their main demographic implications.n n n n